1. Field of the Invention
The present invention relates generally to the study of congenital malformation. More specifically, the present invention relates to methods of preventing diabetes-related congenital malformation.
2. Description of the Related Art
Each year in the United States, about 150,000 babies—3% of all live births are born with a major congenital malformation. This problem is worse in offspring of women who have type 1 or 2 diabetes; 6%-10% of these babies are born with a major congenital malformation. Based on the National Health and Nutrition Examination Survey conducted during 1988-1994, 1.1% of women 20-39 years of age have type 1 or 2 diabetes, and the incidence of diabetes among women of childbearing age has been increasing over the past four decades. It is projected that the number of women of childbearing age with type 2 diabetes will double by 2010, suggesting that approximately 8,000 babies will be born each year in the United States with a congenital malformation secondary to type 1 or 2 diabetes.
Human observational studies have demonstrated a strong link between the extent of a mother's glycemic control and the incidence of congenital malformations in her offspring. The putative teratogenic effects of hyperglycemia are supported by studies that demonstrate a reduction in the incidence of birth defects following clinical intervention targeted at achieving euglycemia. When euglycemia is successfully maintained periconceptionally and during the first trimester, the prevalence of malformations is reduced to a level comparable to that of the general population. However, even with excellent compliance and clinical care, euglycemia may be difficult to achieve and maintain. In addition, it is possible that organogenesis can be affected by short periods of hyperglycemia that are not reflected in the averaged values of glycosylated hemoglobin levels, which are used to monitor glucose levels. A further obstacle is that most women with diabetes do not seek preconceptional care and most have unplanned pregnancies. Hence, a very important goal for public health is to develop and implement accessible intervention strategies to diminish the occurrence of these anomalies.
Both clinical cases and animal studies have clearly demonstrated that the main characteristics of maternal hyperglycemia-associated defects are organogenesis and underdevelopment. The organ systems most commonly affected include the central nervous, cardiovascular, gastrointestinal, craniofacial, genitourinary, and skeletal systems. Because the neural folds and heart develop early during embryogenesis, a higher incidence of malformations is often seen in these organs. In the central nervous system, abnormalities can be categorized as underdevelopment of the midbrain and hindbrain and failure of the neural tube to close at both anterior (rostral) and posterior (caudal) ends of the neural axis. The failure of posterior neural tube closure results in spina bifida, a common birth defect seen in newborns.
Convincing evidence from clinical and experimental studies demonstrates that diabetes-related hyperglycemia leads to sustained generation of reactive oxygen species (ROS) and depletion of antioxidant defense, resulting in intracellular oxidative stress due to an imbalance in intracellular reduction-oxidation (redox) homeostasis. Under normal physiological conditions, oxygen free radicals, including hydroxyl radicals, superoxide anions, singlet oxygen, and hydrogen peroxide (H2O2), are produced during cellular energy metabolism in sub cellular organelles such as mitochondria. The reactive oxygen species mediate intracellular signal transduction that regulates a wide range of cell functions, including proliferation, differentiation, and migration. However, under pathological conditions, excess reactive oxygen species can oxidize proteins, lipids, and DNA, causing cell injury and even cell death.
Over the past two decades, multiple clinical and experimental studies have evaluated the efficacy of maternal dietary supplements to decrease the rate of diabetic embryopathy. Supplements that potentially alter the underlying hyperglycemia-induced increases in oxidative stress, decreases in antioxidant defense, and alterations in membrane lipid metabolism are most relevant.
Lipoic acid and vitamin C reduce reactive oxygen species-mediated effects and support generation of other antioxidants. Lipoic acid is a naturally occurring antioxidant that is an effective scavenger of free radicals. In experimental models, lipoic acid has been shown to reduce malformation rate in diabetic pregnancies from 25% to 10%. In clinical studies of non-pregnant diabetic individuals, lipoic acid lowered the plasma lipid hydroperoxides, demonstrating a decrease in oxidative stress. This effect was maintained even in patients with high glucose levels. Vitamin C is a hydrophilic molecule that can scavenge several free radicals, including the hydroxyl radical. Experimental studies have demonstrated that vitamin C supplementation reduces the rate of embryonic malformations and embryo resorption.
Dietary supplements containing arachidonic acid (AA) and vitamin E prevent membrane lipid peroxidation and may be beneficial for primary prevention of diabetic embryopathy. In vitro and in vivo experimental studies demonstrated that maternal supplementation with arachidonic acid reduced hyperglycemia-induced aberrant membrane lipid metabolism, suggesting a protective effect. Vitamin E is a major lipid-soluble antioxidant that protects biological membranes from lipid peroxidation. Following a diet supplemented with vitamin E, pregnant diabetic rats have higher serum vitamin E levels and lower embryonic malformation and resorption rates than non-supplemented diabetic rats.
Both N-acetylcysteine (NAC), a cysteine progenitor, and folic acid, a methionine/cysteine precursor, increase glutathione synthesis. In experimental models, supplementation with N-acetylcysteine reduced development of peripheral neuropathy and embryopathy in diabetic rats. This may be due to increase in glutathione synthesis and antioxidant capacity in the cell. It is well accepted that dietary supplementation with folic acid prevents neural tube defects in both experimental and clinical models. In diabetic rats, folic acid levels are especially low in the heart, brain, kidney, and muscle.
For each supplement discussed, lipoic acid, vitamin C, arachidonic acid, vitamin E, N-acetylcysteine, and folic acid, animal and human studies have demonstrated that each nutrient is lower among diabetic individuals than non-diabetic individuals. Clinical trials among diabetic patients have demonstrated that a reduction in diabetic complications (i.e., glycemic control, neuropathy, nephropathy, retinopathy, vasculopathy) may occur following supplementation with these compounds. Most of the published studies, however, focused on the effects of a single nutrient, and no randomized clinical trials evaluating adjunctive therapy with antioxidants to prevent diabetic embryopathy have been published.
Thus, it is desirable to define an optimal intervention strategy of using combinations of nutrients for primary prevention of maternal hyperglycemia and diabetic embryopathy. The present invention fulfills this long-standing need and desire in the art.